The application, process description and several embodiments of so-called pulsed electrical field (PEF) treatment chambers for mild preservation have been discussed in literature. Examples can be found in U.S. Pat. Nos. 5,690,978, 5,662,031, 5,447,733, 5,235,905 and DE-3.708.775. The treatment can be performed by pumping the product through a chamber in which an intense pulsed electrical field is generated. In case treatment is applied as a mild preservation method it seems that most vegetative micro organisms (bacteria, yeasts and fungi) are inactivated at a level of typically 30 kV/cm at temperatures that are less than required in a conventional heat pasteurization process. After treatment the organisms have been found not to reproduce. The total time of a treatment depends on the pulse duration and shape, the total number of impulses tat are applied during the residence time in the treatment zone and the volume flow rate of product through the chamber. In order to achieve a sufficient intense field strength temporarily, high voltage pulses of typically microsecond duration are generated in an auxiliary electronic pulse generating system.
The total duration of the treatment is typical in the range of 10-300 microseconds and depends on the specific application. When electrical pulse treatment is performed as a mild preservation method the required reduction of microbiological counts, the type of product and the specific contamination have to be considered, It is preferred to apply several pulses within the treatment zone. High electrical fields should be imposed typically for a total duration in the range of 2 to 200 microseconds. For other field of applications of a treatment, as e.g. the enhancement of induced mass transport through biological membranes by electroporation, the required electrical field strength is in general less than 30 kV/cm.
The electrical fields are imposed to the product using an electrode structure to which high voltage pulses are applied. The electrodes are in physical contact with the product and are contained in a mechanical construction through which the product is pumped. The combination of the electrodes, electrically isolating holders and sealing is referred to as treatment chamber. When produce is pumped through this chamber a treatment is performed in the resident period by applying short high voltage pulses to the electrodes at a sufficiently high rate.